This book is written about heterocyclic compounds mainly belonging to Pyridine molecule. Heterocyclic chemistry has been unparalleled progress owing to the biodynamic behavior of various heterocyclic compounds. They are widely distributed in nature and are essential of life; they play a vital role in the metabolism of all living cells. Synthetic heterocyclic chemistry has influenced almost every walk of human life and the synthesized compounds have found their applications in diverse fields as medicine, agriculture and various industrial fields.